scholarly journals Microstructure features and formation mechanism in a newly developed electroslag welding

2021 ◽  
Author(s):  
Tomonori Kakizaki ◽  
Shodai Koga ◽  
Hajime Yamamoto ◽  
Yoshiki Mikami ◽  
Kazuhiro Ito ◽  
...  
Keyword(s):  
Low Temperature ◽  
Weld Metal ◽  
Heat Input ◽  
Acicular Ferrite ◽  
Charpy Impact ◽  
Electroslag Welding ◽  
Weld Metals ◽  
Columnar Grains ◽  
Cooling Speed ◽  
Low Temperature Toughness

AbstractElectroslag welding (ESW) is known to show higher heat input than electrogas welding (EGW), resulting in poor low-temperature toughness. However, a newly developed ESW (dev. ESW) method using low-resistivity slag bath exhibited excellent low-temperature toughness as a result of lower effective heat input than conventional EGW, as demonstrated by the faster cooling rates measured in weld metals and estimated using finite element method analyses. This led to much shallower molten pool in the dev. ESW, resulting in much finer columnar grains and thinner centerline axial grains. High cooling speed in the dev. ESW method appeared to contribute to increased acicular ferrite proportion. The uniform microstructure with large acicular ferrite proportion and small number of inclusions in the weld metal permitted the dev. ESW weld metal to possess little variation in Charpy impact energy across the center of weld metal.

Microstructure Transformation and Mechanical Properties of X80 Large Diameter Thick Wall Induction Heating Bend for Low Temperature Service

2020 ◽  
Author(s):  
Yu Liu ◽  
Zongbin You ◽  
Lijun Yan
Keyword(s):  
Mechanical Properties ◽  
Low Temperature ◽  
Weld Metal ◽  
Acicular Ferrite ◽  
Base Material ◽  
Welding Process ◽  
Seam Weld ◽  
Bent Pipe ◽  
Low Temperature Toughness ◽  
Submerged Arc

Abstract For the requirement of pipeline station construction project, Grade X80 Longitudinally Submerged Arc Welded (LSAW) induction bend pipe 1422 mm in diameter and wall thickness greater than 25 mm have been developed for pipeline station service applications at −45 °C. The mother pipe of the bends was welded by Ni-Cr-Cu-Mo-Nb-V micro-alloyed Thermo Mechanical Control Process (TMCP) steel plates. After the heat cycle of the bent pipe manufacturing, the microstructure of the base material of the bent pipe consisted of lath bainite ferrite (LBF) and granular bainite (GB). Therefore, it can obtain high strength and excellent low temperature toughness, which can meet the requirements of the project. On the other hand, the welding of the longitudinal seam-welds of the bend mother pipe uses a typical multi-wire two-pass submerged arc welding (SAW) process, which has a large amount of welding heat input. This results in a coarse columnar weld structure with a large amount of fine acicular ferrite so that the seam weld still has a good low temperature impact toughness. However, after the thermal cycling of the bend, the acicular ferrite in the microstructure of the weld metal was greatly reduced, and the grain size was unevenly distributed, which caused the low temperature toughness of the weld metal to deteriorate significantly. In order to solve this problem, the Gleeble3500 thermal simulation test machine was used to test the phase transition critical point Ac3 of the base material and the seam weld metal of the mother pipe. In order to optimize the induction bend process parameters, the influence of heating temperature, cooling rate and tempering temperature on microstructure and mechanical properties were examined. In addition, on the basis of the existing welding process, the welding wire and flux for pipe-making seam-welding were improved, and the pipe-making welding process of the bent mother pipe was improved.

Experimental Study on High Performance Welding Materials for Pipeline Steels

2004 ◽  
Author(s):  
Zhijun Huang ◽  
Kai Miao ◽  
Xiudi Cao ◽  
Yutao Wang
Keyword(s):  
Low Temperature ◽  
Charpy Impact ◽  
High Strength ◽  
Alloying Elements ◽  
Charpy Impact Energy ◽  
High Quality ◽  
High Toughness ◽  
Weld Metals ◽  
Low Temperature Toughness ◽  
Welding Materials

West-to-East Natural Gas Transmission Project is in great need of high quality steels of API grade X70 and suitable high quality welding materials. The weld of pipe should have high strength, high toughness and low sulphur and arsenic contents (less than or equal to 0.005 wt % respectively). The work performed in WISCO concerning welding wires of SAW, GMAW and SMAW and weldability of pipe steel is reported in this article. Steel grade X70 is a TMCP high strength and high toughness steel with low carbon equivalent. It has good weldability and is less susceptible to cold cracking in the heat-affected zone. Generally in order for weld to gain the same strength as the base metal, more alloying elements should be added into the weld. Therefore, it is likely that the weld is expected to be more susceptible to cold cracking. The mechanism of strengthening and toughening of the weld should be carefully investigated. WISCO has made great progress in both property improvement and manufacturing of welding materials. Through the addition of alloying elements, the influences of some alloying elements on the strength and toughness of welds, especially on the low temperature toughness were carried out. The results show that the upper shelves of the Charpy V transition curves for the weld metals remain high despite the different alloying elements. However, the influence of alloying degree on the low-temperature toughness is significant. The weld metals micro-alloyed with Ti,B and Ni, etc. have high acicular ferrite volume fractions in the metallographs, thereby possessing high strengths and high toughness. For SAW weld, the strength is more than 590MPa, the Charpy impact energy at −40°C above 180J; for the weld of gas metal arc welding, the Charpy impact energy at −30°C reaches 190J which are far better than some current specifications. If the welding is performed with caution, no cracks were found. HIC and SSCC test for corrosion resistance of the welds were also performed and the results fully met the requirements concerned. With respect to strength and toughness, chemistry and metallography, the HIC performance of welds was analysed.

Microstructure and Impact Toughness of Flux-Cored Arc Welded SM570-TMC Steel at Low and High Heat Input

2020 ◽  
Vol 991 ◽  
pp. 3-9
Author(s):  
Herry Oktadinata ◽  
Winarto Winarto ◽  
Eddy S. Siradj
Keyword(s):  
Low Temperature ◽  
Impact Toughness ◽  
Base Metal ◽  
Heat Input ◽  
Charpy Impact ◽  
Cored Wire ◽  
Average Heat ◽  
Weld Metals ◽  
Flux Cored Arc Welding ◽  
The Impact

This work investigated microstructure and impact toughness of multi-pass flux-cored arc welded SM570-TMC steel. A comparison was made between weldments fabricated with average heat input of 0.9 kJ/mm and 1.4 kJ/mm, respectively. SM570 steel plate with 16 mm nominal thickness and 1.2 mm diameter of E81-Ni1 flux-cored wire were selected in this experiment. Multi-pass flux-cored arc welding (FCAW) was performed using carbon dioxide shielding gas. Then the weldments were observed using optical microscopy, scanning electron microscope (SEM) and electron probe micro analyzer (EPMA). The steel joint strength was measured via tensile test, and Charpy impact test was performed at three different test temperatures. The microstructure observation exhibited the base metal mainly consist of ferrite and pearlite features, while the weld metal contained the acicular ferrites, polygonal ferrites and M-A constituent at both different heat inputs. The impact toughness of base metal is superior than weld metals. The weld metals fabricated at average heat input of 0.9 kJ/mm have a higher low temperature impact toughness than using heat input of 1.4 kJ/mm. The acicular ferrites amount that significant reduced at the higher heat input may degrade the toughness at low temperature.

Effects of Inclusions and Microstructures on Impact Energy of High Heat-Input Submerged-Arc-Weld Metals

2005 ◽  
Vol 127 (2) ◽  
pp. 204-213 ◽  
Author(s):  
Beomjoo Kim ◽  
Sangho Uhm ◽  
Changhee Lee ◽  
Jongbong Lee ◽  
Youngho An
Keyword(s):  
Weld Metal ◽  
Impact Energy ◽  
Heat Input ◽  
Acicular Ferrite ◽  
Charpy Impact ◽  
High Heat ◽  
Charpy Impact Energy ◽  
Number Density ◽  
Average Size ◽  
Submerged Arc

Submerged-arc-weld metal made with variations of heat-input and consumables were examined to study the inclusions and their effects on the Charpy impact energy of the weld metal as a measure of the toughness. From the analysis, inclusions, of which diameters were smaller than 2 μm, seemed to be effective for acicular ferrite nucleation and the fraction of acicular ferrite was in proportion to the number density of inclusions <2 μm. However, as the heat input increased, the average size of inclusions increased but their number density decreased. It was also observed that the grain sizes of polygonal ferrite with increased heat input. Accordingly, the decrease of the Charpy impact energy with the heat input is inevitable due to these microstructural changes. But, this does not mean that the acicular ferrite cannot be nucleated.

Effects of oxygen content on microstructure and impact toughness of high heat input flux-cored wire weld metals

2018 ◽  
Vol 115 (4) ◽  
pp. 410
Author(s):  
Fengyu Song ◽  
Yanmei Li ◽  
Ping Wang ◽  
Fuxian Zhu
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Weld Metal ◽  
Oxygen Content ◽  
Heat Input ◽  
High Heat ◽  
Cored Wire ◽  
Weld Metals ◽  
High Heat Input ◽  
The Impact

Three weld metals with different oxygen contents were developed. The influence of oxygen contents on the microstructure and impact toughness of weld metal was investigated through high heat input welding tests. The results showed that a large number of fine inclusions were formed and distributed randomly in the weld metal with oxygen content of 500 ppm under the heat input condition of 341 kJ/cm. Substantial cross interlocked acicular ferritic grains were induced to generate in the vicinity of the inclusions, primarily leading to the high impact toughness at low temperature for the weld metal. With the increase of oxygen content, the number of fine inclusions distributed in the weld metal increased and the grain size of intragranular acicular ferrites decreased, which enhanced the impact toughness of the weld metal. Nevertheless, a further increase of oxygen content would contribute to a great diminution of the austenitic grain size. Following that the fraction of grain boundary and the start temperature of transformation increased, which facilitated the abundant formation of pro-eutectoid ferrites and resulted in a deteriorative impact toughness of the weld metal.

Effect of Chemical Composition of Welding Wire and Low Temperature Steel Plate on the Weld Properties Made by SAW

2008 ◽  
Vol 580-582 ◽  
pp. 57-60
Author(s):  
Hee Joon Sung ◽  
Yeon Baeg Goo ◽  
Kyeong Ju Kim ◽  
Kee Young Choi
Keyword(s):  
Chemical Composition ◽  
Low Temperature ◽  
Weld Metal ◽  
Steel Plate ◽  
Butt Joint ◽  
Welding Wire ◽  
High Hardenability ◽  
Weld Metals ◽  
Weld Properties ◽  
Mo Content

Chemical composition effect on the weld properties for low temperature steel was evaluated. The alloy elements of interest at the weld metal were Cr and Mo, which come from the steel plate and welding wire, respectively. Both side one run SAW process was carried out in a Ygroove butt joint. Microstructure of the weld metal is strongly dependent on the chemical composition of the steel plate and the welding wire, due to high dilution. The microstructure of the weld metal became fine acicular ferrite by increasing Cr and Mo content because of high hardenability effect. The weld metal having Cr and Mo possessed the highest impact toughness at low temperatures among the weld metals studied. Cr seems to have more effect than Mo on the toughness of the weld metal.

scholarly journals The influence of the oxygen equivalent in a gas-mixture on the structure and toughness of microalloyed steel weldments

2006 ◽  
Vol 71 (3) ◽  
pp. 313-321 ◽  
Author(s):  
Radica Prokic-Cvetkovic ◽  
Andjelka Milosavljevic ◽  
Aleksandar Sedmak ◽  
Olivera Popovic
Keyword(s):  
Impact Toughness ◽  
Crack Propagation ◽  
Weld Metal ◽  
Acicular Ferrite ◽  
Microalloyed Steel ◽  
Gas Mixtures ◽  
Gas Mixture ◽  
Weld Metals ◽  
Maximum Crack ◽  
The Impact

Testing were carried out on two steels. The first was microalloyed with Nb and second with Ti, Nb and V. The impact toughness of weld metals of these steels was evaluated using an instrumented Charpy pendulum. Five different gas mixtures (Ar, CO2, O2) were used to determine the optimal gas shielded metal arc process for both steels. The oxygen equivalent was used as a representative parameter of a mixture to follow, in particularly, its effect on the microstructure, toughness and crack propagation energy of the weld metal. For these investigated steels, the optimum gas mixture was established (5%CO2, 0.91%O2, balance Ar), which provided the maximum crack propagation energy, due to the microstructure which consisted dominantly of acicular ferrite.

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